It's better for her to apply for a single-entry visa permitting 4 months stay duration in China, if she gets a double-entry visa, she has to exit Mainland China when the stay duration per entry is up. However, the duration of stay of a "L" visa is 30 days, which means the holder of the visa may stay in China for up to 30 days from the date of entry. If her estimated stay in China is longer than 30 days, please make it clear in the application form and ask for the Visa Officer's approval when she submit her application. It is also Ok for her to apply for visa extension at the Publci Security Bureau after she enters China.